1. Field of the Invention
The present invention is generally concerned with clutches, especially for automobile vehicles, and is more particularly directed to clutches for large automobile vehicles.
2. Description of the Prior Art
The clutch fitted to a large vehicle is more often than not a mechanical clutch, meaning a clutch which, for clamping a clutch plate against a reaction plate, comprises a spring-loaded mechanism, a diaphram mechanism, for example, with which there is associated a controlling actuator member, usually called the clutch release bearing, movable substantially along its axis.
Given the masses involved and the torque to be transmitted, a high force has always to be applied to operate the clutch of a large vehicle, in other words to move the clutch from its engaged condition with the clutch plate clamped up to its disengaged condition with the clutch plate released, to change the gear ratio, for example. In other words, a high force has always to be applied to the corresponding actuator member to move it axially sufficiently to bring about this change in the state of the clutch.
In practice, this force is more often than not in excess of 500 Newtons.
On a large vehicle the clutch must normally be power-assisted.
Some large vehicles have no onboard source of pressurized fluid (compressed air or hydraulic fluid) to provide such assistance, however.
In this case the clutch is often not a mechanical clutch in the sense defined above, but an electromagnetically operated centrifugal clutch, comprising flyweights responsive to centrifugal force for clamping up a clutch plate.
A major disadvantage of a clutch of this kind is its long response time.
To change the gear ratio takes the time added to energize the electromagnetic part, for the centrifugal part to drop out, for the new gear ratio to be selected, for the electromagnetic part to be de-energized and for the centrifugal part to be deployed.
Overall this may take several seconds.
This may cause problems, especially on slopes, to the detriment of the maneuverability and safety of the vehicle concerned.
Also, given their complexity, electromagnetically operated centrifugal clutches often have the further disadvantage of being relatively costly.
A general object of the present invention is an arrangement enabling these disadvantages to be avoided and thus making it possible to procure under good conditions, especially from the economic point of view, the control of a clutch of a large vehicle with no onboard source of pressurized fluid, while advantageously exploiting specific arrangements usually characterizing a vehicle of this kind.